Optical fiber ribbon cables are well known for the transmission of optical signals. Use of optical cables, including optical fiber ribbon cables, has generally been limited to long-haul trunking installations where the improved transmission characteristics of the optical fibers justify the greater expense and difficulty associated with their manufacture and installation. As the demands on communication media continue to increase, the advantages of using optical cable for transmission of signals across shorter distances or, for interconnecting local devices, continues to grow. Unfortunately, the costs associated with the production of optical fiber cable assemblies, and in particular with the installation of connectors on optical fiber ribbon cables, continue to limit the wide spread application of optical fiber transmission media for these applications.
Traditionally, a single fiber optical cable is assembled by coating an optical fiber with a buffer layer and then encasing the buffered optical fiber within a Kevlar.RTM. sheath that provides tensile strength and a vinyl outer jacket that serves as an environmental shield. Multi-fiber optical cables are assembled in a similar manner by bundling multiple buffered optical fibers within the center of a Kevlar.RTM. sheath and corresponding outer jacket. The difficulty with a multi-fiber bundled optical cable is in providing an economic, convenient and reliable system for installing a connector on the ends of the optical fibers so as to provide a finished fiber optic cable assembly.
As an alternative to a multi-fiber bundled optical cable, optical fiber ribbons have been developed in which multiple optical fibers are aligned and maintained in a planar configuration. U.S. Pat. No. 3,920,432, issued to Smith describes an early method of fabricating an optical fiber ribbon cable in which a plurality of glass optical fibers are carried by a grooved holder with a plurality of spacing fibers of triangular cross-section continuously fed into the spaces between adjacent optical fibers in the holder. The spacing fibers are then melted to secure the optical fibers within the holder. The advantage of this technique is that the optical fibers are accurately aligned within the holder, thereby aiding in the ability to easily interface the fiber optic ribbon with an optical connector. The disadvantage is that this technique limits the mechanical performance of the fiber optic ribbon by requiring that the holder be provided for the entire length of the ribbon and that the holder have sufficient structural integrity to accurately maintain the positioning of the optical fibers within the holder. In addition, the requirement that the fiber optic ribbon be heated in order to melt the triangular-type spacing fibers to secure the optical fibers within the holder subjects the fiber optic ribbon to thermal stress.
U.S. Pat. Nos. 4,289,558 issued to Eichenbaum et al. and 4,980,007, issued to Ferguson describe improved methods of fabricating a fiber optic ribbon in which buffered optical fibers are positioned adjacent one another in a planar orientation and then sandwiched between the adhesive layers of a pair of thin binding tapes. The resulting fiber optic ribbon is then encased in Kevlar.RTM. fibers and a plastic sheath, for example, to provide tensile strain relief and environmental protection for the optical fibers. In this technique, the alignment of the optical fibers within the ribbon is created and maintained by abutting adjacent fibers and then relying on the dimensional characteristics of the buffer layer surrounding the optical fibers so as to achieve a uniform spacing across a cross sectional width of the fiber optic ribbon. While these techniques provide a clear manufacturing advantages to the technique disclosed by Smith in U.S. Pat. No. 3,920,432, the problems which are created by utilizing these techniques are an increased difficulty in attaching, aligning and installing optical connectors on the ends of the fiber optic ribbon in order to create a finished fiber optic ribbon cable assembly.
Numerous optical connectors have been developed to aid in the connection and splicing of fiber optic ribbons. Examples of connectors which are designed to terminate an end of a fiber optic ribbon are shown and described in U.S. Pat. Nos. 3,864,018, issued to Miller, 4,793,683, issued to Cannon, Jr., et al., and 5,309,537, issued to Chun, et al. In contrast, U.S. Pat. No. 3,871,935, issued to Cloge, et al. and European Patent Publ. No. 0 613 031 81 both describe methods for encapsulating a middle portion of a fiber optic ribbon within an optical connector assembly that is then severed in half to form opposed ends of a pair of optical connectors. In both of these references, the protective jacket and buffer surrounding the optical fibers are chemically removed in a middle portion of the ribbon and the resulting bare optical fibers are positioned within an encapsulating mold into which a bonding material is injected to secure the optical fibers. Once secured, the molded assembly is divided in half along a plain perpendicular to the axis of the optical fibers, thereby exposing ends of the fibers which can be polished for alignment and/or abutment to other optical fiber ends. The advantages of these encapsulation connector techniques are that they involve less manipulation and mechanical stress of the optical fibers than the technique taught by Smith. The disadvantages are that the stripping step subjects the optical fibers to potential damage and that the alignment of optical fibers in the molded assembly is not certain due to the potential movement of optical fibers during the encapsulating process. In any event, these techniques are still post-production techniques applied after the fiber optic ribbon has been assembled.
Although existing techniques for the manufacture of fiber optic ribbon cable assemblies having optical connectors at one or both ends of a fiber optic ribbon cable are capable of producing optical transmission media that are well suited for certain applications, it would be desirable to provide a method of fabrication of fiber optic ribbon cable assemblies which was more cost effective and allowed for easier manufacture and assembly of fiber optical ribbon cable assemblies so as to broaden the potential applications for use of fiber optic ribbon cables.